The present invention generally relates to integrated circuit (xe2x80x9cICxe2x80x9d) operational amplifiers. More specifically, the invention relates to cascode, two-stage operational amplifiers.
Since the development of the transistor and integrated circuits, IC operational amplifiers (xe2x80x9cop-ampsxe2x80x9d) have been used in many applications related to such fields as telecommunications, audio/video technology, and computers. Complementary metal oxide semiconductor (xe2x80x9cCMOSxe2x80x9d) operational amplifiers are a major category of IC op-amps that are used in a variety of applications. For example, CMOS op-amps are widely applied in high performance CMOS circuits, such as high speed/high resolution pipeline analog-to-digital (xe2x80x9cA/Dxe2x80x9d) converters.
In the application of op-amps, such as CMOS op-amps, the performance of the overall circuit is typically limited by the performance capability of the op-amp(s) used in the circuit. For example, the dynamic range performance and frequency response performance of a circuit using an op-amp are generally limited based on the open-loop DC gain and unity-gain frequency of the op-amp. High performance circuits require op-amps with high open-loop DC gain and a high unity-gain frequency.
There have been continuous efforts made to develop op-amps with higher open-loop DC gain and a higher unity-gain frequency to support the development of increasingly higher performing circuits. Typically, in this regard, there are prominent trade-offs that occur in op-amp performance. For example, an increase in gain performance typically results in an undesired decrease in frequency response performance. As another example, an increase in speed/unity-gain frequency typically results in the undesired increase of power consumption.
Various op-amp designs have been developed in an attempt to meet high performance requirements while minimizing performance trade-offs. These designs include folded-cascode op-amps with gain boosting and two-stage op-amps. Designs denoted by these names are known in the art, and need not be described herein. Yet, such designs have not been shown to fulfil the increasing demand for even higher performance applications. Thus, there is a need for an operational amplifier that performs with very high open-loop DC gain while maintaining a very high unity-gain frequency, in comparison to existing designs, but without significant increase of undesired parameters.
Certain objects, advantages, and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve various objects and advantages, the present invention is directed to a novel op-amp circuit. In accordance with a preferred embodiment of the present invention, a two-stage op-amp circuit including a double-cascode telescopic op-amp circuit in the input stage and a fully-differential op-amp circuit in the output stage is provided.
One advantage of a preferred embodiment of the present invention is that it performs with a very high open-loop DC gain in comparison to existing op-amp circuits. Another advantage of a preferred embodiment of the present invention is that its significant increase in open-loop DC gain does not result in a decrease in its unity-gain frequency, as typically occurs in existing op-amp circuits. That is, a preferred embodiment of the present invention performs with a very high open-loop DC gain while also maintaining a very high unity-gain frequency. Yet another advantage of a preferred embodiment of the present invention is that, considering its very high open-loop DC gain and very high unity-gain frequency performance, it has no increase in power consumption and a significantly small increase in other undesirable operation parameters in comparison to existing op-amp circuits.
Other objects, features, and advantages of the present invention will become apparent to one skilled in the art upon examination of the following drawings and detailed description. It is intended that all such additional objects, features, and advantages be included herein within the scope of the present invention, as defined by the claims.